Beneficiation of nonmetallic ores



Patented Feb. 19, 1952 r 2,588,545 nanarrcm'rlon or NONMETALLIC ORES 1in: Milton Le Baron, Lakeland, Walter 0. McClintock, Mulberry, and JamesE. Lawvcr,

Lakeland, Fla., assignors to International Minerals and ChemicalCorporation, a corporation of New York No Drawing. Application June 31947,

Serial No. 752,272

5 Claims. (01. 209-8) The present invention relates to the beneficiationof non-metallic ores and is applicable in particular to phosphate oressuch as those found in Tennessee and Montana. The novel processhereinafter described is applicable for the beneficiation of anyphosphatic ores in which the iron values are differentially associatedeither with the gangue or with the phosphate values as the case may be.I

The phosphate industry requires, for the production of superphosphateand for the production of triple superphosphate, a phosphatic rock ofrelatively high B. P. L. (bone phosphate of lime) value and imposespenalties where impurities, such as iron compounds, alumina, etc., arepresent in excess of minimum fixed percentages. Previous processes ofbeneficiating non-metallic ores in which group phosphate rock iscommonly classified have resulted in successfully meeting thesestandards of B. P. L. content, but it has been found that such processesas tabllng and flotation, while successful in a large number of cases,are nevertheless quite expensive to operate because of the initial costof machinery and because of the subsequent operating and maintenancecosts. Also, in these previously used processes of beneficiating, therequired chemical reagents employed for pretreating the phosphatic oresare quite expensive. In cases where the ores are associated with largequantities of slimes, the consumption of these expensive reagents islikewise materially increased over that required with ores having arelativelysmall amount of slime. In flotation and tabling processes asnow conventionally employed, the increased amounts of these costlyreagents used may be not only required because of large quantitles ofslime which may be originally present in the ores processed, but alsorequired because in the process of working the ores from step to step tobeneficiate the same, further amounts of slime are inherently produced.Because of this, an additional quantity of costly reagents must be addedto compensate for the increased production of slimes. In addition thesereagents must be added at the proper stages in the processing if theyare to be efilcaciously utilized.

It is an object of the present invention to produce beneflciatedphosphatic ores of high B. P. L. content and with relatively low ironcompounds, alumina, etc. content from relatively low grade phosphateores containing undesirable amounts of iron compounds, alumina and otherimpurities.

It is a. further object of the present invention to obviate thenecessity for using expensive reagents in the beneflciation ofphosphatic ores while at the same time producing concentrates of suchores which meet the accepted requirements of purity for the phosphateand fertilizer industries.

It is a further object of the invention to produce high grade phosphaticore concentrates ,while avoiding the use of excessive amounts ofelectrical power, machinery, maintenance and other operating costsheretofore considered necessary to accomplish this result.

It is a still further object of the invention to beneficiate thenon-metallic ore, such as phosphatic ore, having undesirable amounts ofiron compounds, alumina and other impurities to meet the requiredstandardsregardless of the particular particle size or the uniformity ofthe ore particles processed so long as the individual particles aresufficiently comminuted to give separation of the desired values.

Other objects will be apparent upon a fuller understanding of theinvention as hereinafter more completely described.

It has been discovered that any non-metallic I ore containing ironcompounds disproportionally associated with the various components ofthe ore may be subjected to a segregation treatment so that variousvalues of the ore may be beneficiated or concentrated with respect toone another by passing such an ore which has been previously roasted ina reducing atmosphere through a magnetic field, one or more times. In sodoing, the non-magnetic and magnetic portions so separated are found tobe beneflciated with respect to the phosphatic content. In some ores thegreater part of the phosphatic content is magnetically associated withthe iron compound. In other ores the magnetic impurities aredifferentially separated from the greater part of the phosphatic values.The roasting and subsequent magnetic treatment may be variedconsiderably. If more than one passage is carried out, the intensity ofthe magnetic field is generally increased, though not necessarily so, asbetween the first magnetic field and subsequent fields.

In the case of such treatment of a Tennessee phosphate rock (brownrock), whichhas been roasted in a reducing atmosphere, a markedbeneficiation of the ore may be effected by passing the reduced orethrough a magnetic field of relatively low intensity which gives aseparation of the ore into a product which is high in iron compounds,alumina and other impurities and somewhat higher in phosphatic values.This second assaus product in turn may then be passed through a magneticfield of much higher intensity than the first field used which resultsin. a second substantially non-magnetic product being quite low in ironcompounds, alumina, and in other impurities and quite low in phosphaticvalues with the magnetic product, having intermediate amounts of ironcompounds, alumina and other impurities, but containing high phosphaticvalues.

A similar treatment of iron-containing Montana phosphate ore indicatesthat .it behaves somewhat differently from the Tennesseephosphate ore.However, the principle of operation involved is the same. The Montanaore has the same disproportionate association of iron values withrespect to the other constituents of the ore so that it is possible toremove iron and at the same time beneficiate the phosphatic values.Montana phosphate rock, upon being roasted in a reducing atmosphere andsubjected to a magnetic field, yielded after a first passage atarelatively low intensity of magnetism a first product quite high in ironcompounds, alumina and other impurities,

and quite low in phosphate content with the nonattracted portion beingof increased phosphatic value and decreased impurity content. Thisnonattracted portion may he then subjected to a magnetic field ofrelatively higher intensity resulting in a magnetically attractedproduct having intermediate amounts of iron compounds, alumina and otherimpurities and a. substantially non-magnetically attracted portion ofvery low iron content, alumina and other impurities but of very highphosphatic content.

Various modifications of the above described process are possible. Forexample in processing Montana phosphate ore, the magnetically reducedore may be initially subjected to a relatively high intensity magneticfield to give a separation or segregation of an attracted portion ofhigh iron compounds, alumina and other impurities and relatively lowdesired non-attracted product of low iron compounds, alumina and otherimpurities but having a very high phosphate content. If desired thisattracted portion may be resubjected to a magnetic field of lowerintensity and a non-attracted, portiontherefrom admixed with thenon-attracted portion first produced. Although the once-through magnetictreatment may be advantageously employed with reference to Montana rock,this type of treatment, while it may be employed for Tennessee phosphaterock. is not generally advantageous because itgives poor results so faras phosphatic beneficiation is concerned. Depending upon the propertiesof any particular phosphate iron-containing ore, one or several passagesthrough the magnetic field at the same or varying magnetic intensitiesmay be employed. Still a further variation in the procedure involvessubjecting the roasted ore. the originally attracted fractions and/orthe originally non-attracted ores to subsequent magnetic fields whichmay be of either higher or lower intensities than that employed in thenext preceding-magnetic treatment, with the exception that littleadvantage is to be gained, generally speaking, in subjecting thefraction previously attracted under a low intensity magnetic field to asubsequent higher magnetic field without some intermediate treatment.

As previously indicated, in order to successfully practice thenovel'process herein outlined, the particular phosphatic ore processedmust contain iron compound impurities disproportionately associated withthe various other chemical constituents, and in addition, this ore,prior to its actual beneficiation, must be roasted in a reducingatmosphere. Generally speaking, the particular temperature, time ofreaction, and other roasting conditions used, depend upon the averageparticle size of the ore, the physical characteristics of the oreparticle, the chemical content of-the ore, and in addition, depend uponthe ore being sumciently comminuted to free the particles containing theimpurities from the particles of the desired phosphatic values. Ingeneral, it has been found that a phosphate rock containingsubstantially free particles may be successfully processed according tothe novel process, if the sizing is between "1" in diameter and aboutplus 200 mesh. Such an ore generally will require between about 15 andabout '70 minutes roas time at a temperature between about 750 and 1350"F. A reducing atmosphere is employed d g the roasting so as to insurethe conversion 0 substantlally all of the iron-bearing compounds presentin the ore into a magnetic iron oxide. A reducing atmosphere is insuredif the roasting chamber contains a reducing agent such as carbon, carbonmonoxide, hydrogen or any other convenient material of similar reducingproperties. These reducing materials may be added in any convenientform, that is, as gases, liquids or solids.

It is desirable, though not absolutely necessary, to efiect apre-treatment of the ore with a. dilute mineral acid such ashydrochloric or sulfuric acid before subjecting the ore to the reducingroast. The ore treatment with dilute acid effects a desliming, in whichcase there is also an upgrading of the B. P. L. content of the ore withan incidental removal of considerable amounts of aluminum oxide. Aspreviously mentioned, it is also desirable, at times, to grind orotherwise comminute the ore particles so as to free the particlesinsofar as possible into individual units for efficiently processingprior to the acid desliming or reducing roast treatments.

The ore, after roasting under reducing conditions, is then subjected tothe action of a magnetic field. In the manner previously explained,

being varied between about 1" and about 54;".

It is obvious, of course, that magnets and magnetic fields of varioussizes, strengths, and spacings between the magnetic poles of varieddistances outside the figures stated, may be employed with the proper afiustments being made for the particular ore particles being processed.Although direct current magnets were employed in the specific runshereinafter described, alternating magnets may also be used if desired.Various commercially-available magnetic separators may be employed.These are already marketed and available for ore dressing operations, inconnection with the beneficlation' of the metallic ores.

The following specific examples are only illustrative of the nature andcharacter of the invention, and it is not intended that the invention belimited hereo.

Example 1.A sample of a Tennessee brown phosphate rock was washed withconcentratedv was added in the amount corresponding to about 3 lbs. of100% sulfuric acid per ton of rock fed. Alternatively, up to 4 lbs. perton of feed of any suitable mineral acid such as, for example,hydrochloric acid or sulfuric acid also could be used though not in allinstances is it necessary to employ a pre-acid treatment. The acidifiedrock was agitated for about 5 minutes and then deslimed by water washingand draining. The ma terial was then dried and subjected to a roastingoperation under a reducing atmosphere at a temperature of about 1000 F.for about one hour. The reducing atmosphere was provided using woodcharcoal. The roasted product was then cooled and subjected to amagnetic separation using a magnetof 3000 ampere turns. The materialcontacted the poles of the magnet. The magnetic product was 25 weightper cent. of the material treated and had about 61.25% Bf P. L., about11.7% insoluble and about 12.6% iron oxide and alumina. The non-magneticportion of the material constituted about 75 weight per cent of thematerial treated and contained about 70.36% B. P. L., about 10.8%insoluble and about 5.03% iron oxide and alumina. The original feedcontained about 68.0% B. P. L., about 11.02% insolubles and about 6.92%iron oxide and alumina. Even in the presence of such a weak magnet thenon-magnetic portion of the product showed an upgrading of B. P. L.content with a marked lowering of iron compounds and alumina. In thefollowing examples, a much stronger magnetic field was employed.

Example 2.A Tennessee brown phosphate rock was treated with sulfuricacid in accordance with the description shown in Example 1. The washedore analyzed as follows:

Weight per cent B. P. L. 63.69 Insolubles 20.26 Iron oxide and alumina5.60

Per Cent Iron 6:

Weight P- Ins1 Alumina Feed to Magnet 100. 0 63. 69 20. 26 5. 60 HighlyMagnetic Product 12. 2 62.54 12. 95 14. 02 Weakly Magnetic Product. 46.2 72. 86 9.32 i 4. 68 Non-Magnetic Product. 40. 6 54. 92 33. 54 2. 07

An inspection of the data shows that the weakly magnetic product wasbeneficiated in B. P. L. content from 63.69 weight per cent up to 72.86weight per cent, the acid insolubles dropped from 20.26 weight per centto 9.32 weight per cent and the iron oxide and alumina content droppedfrom an original value of 5.6 weight per cent to 4.68 weight per cent.The product so produced is acceptable to the trade for use in thephosphate industry whereas the original material processed is not soaccepted.

Example 3.A sample of Montana phosphate rock was crushed and then groundin a ball mill to minus 48 mesh and the minus 150 mesh portion Per centIron 6:

weight Insol' Alumina Feed to Magnet 100.0 63. 61 14.41 3. 23 HighlyMagnetic Product 41. 6 50. 72 25. 5. 54 Weakly Magnetic Product 15. 768. 26 13.10 2.00 N on Magnetie Product 42. 7 74. 57 7. 60 i. 20

In contrast to the results obtained in magnetically beneficiatingTennessee phosphate rock wherein the weakly magnetic fraction was thedesired portion of the feed as indicated in Examples 1 and 2, in theinstant example wherein Montana phosphate rock was similarly processed,the desired portion of the feed was isolated as the non-magneticfraction. Thus it is clear from the data shown in this example that theweight per cent B. P. L. was increased from 63.61% to 74.57%, the acidinsolubles dropping from a weight per cent of 14.41% to 7.60% and theiron oxide and alumina dropping from a weight per cent of 3.23% to1.20%. This product likewise is readily saleable to the phosphate rockindustry.

Example 4.Another sample of Montana phosphate rock was preliminarilyprocessed in similar manner to that described in Example 3, similarlyroasted under reducing conditions and subjected to magnetic separationusing the same magnet employed in Examples 2 and 3. The fraction andanalysis thereof were as follows:

Per cent Iron (in weight B. P. L. Insol. Alumina Feed to Magnet 100.075.07 9.30 3.02 Highly Magnetic Product 2. 0 46. 55 23. 75 15. 20 WeaklyMagnetic Product ll. 0 63. 28 20. 56 5. 06 Non-Magnetic Product 87. 081. 12 6. 22 1.48

In the run, the non-magnetic portion constituted about 8'7 weightpercent of the feed with the weight percent of B. P. L. rising from75.07% to 81.12%, the acid insoluble portion weight percent decreasingfrom 9.3% to 6.22% and the weight percent of iron oxide and aluminadecreasing from 3.02% to 1.48%. This is a high grade product readilysaleable to the phosphate stars in the range oi between about 750 F. andabout 1350 FL, and subjecting the roasted ore to magnetic separation toproduce at least a phosphate traction low in iron content.

2. A process for beneficiation of iron compound-containing Tennesseephosphate rock having the iron compounds unevenlydispersed through thephosphate material as a component which economical comminution methodsfail to liberate, which comprises desliming the comminuted ore, roastingthe comminuted ore in areducing atmosphere at a temperature in the rangeof between about 750 F. and about 1350 F., and subjecting thev roastedore to magnetic separation to produce at least a phosphate traction lowin iron content. 4

3. A process for beneflciation of iron compound-containing Montanaphosphate rock having the iron compounds unevenly dispersed through thephosphate material as a component which economical comminution methodsfail to liberate, which comprises desliming the comminuted ore, roastingthe comminuted ore in a reducing atmosphere at a temperature in therange of between about 750 F. and about 1350 F., and subjecting theroasted ore to magnetic separation to produce at least a phosphatefraction low in iron content. c

4. A process of beneflciating iron compoundcontaining Tennessee brownphosphate ore which comprises desliming comminuted ore with dilutesulfuric acid, roasting said deslimed ore under reducing conditions at atemperature of between about 750 F. and about 1350 F., subjecting saidore to mild magnetic separation, subjecting the non-attracted fractionto a magnetic separation or increased magnetic intensity over that ofthe first magnetic separation and recovering a fraca I tion in thesecond instance as a desired phosphate traction low in iron content.

5. A process 0! beneflciating iron compoundcontaining Montana phosphaterock which comprises desliming comminuted ore with dilute sulfuric acid,roasting said deslimed ore under reducing conditions at a temperature ofbetween about 750 F. and about 1350 F., subjecting said ore to mildmagnetic separation, subjecting the non-attracted fraction to a magneticseparation 01 increased magnetic intensity over that of the firstmagnetic separation and recovering a fraction in the second instance asa desired phosphate traction low in iron content.

I. MILTON LE BARON. WALTER O. McCLIN'I'OCK. JAMES E. LAWVER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,914,695 Lange June 20, 19332,373,688 Keck Apr. 17. 1945 FOREIGN PATENTS Number Country Date 274,889Great Britain Apr. 12, 1928 OTHER REFERENCES Publication by F. Y.Fe'rney in Chemical and Metallurgical Engineering," vol. 43 (1936),pages 23, 24, copy of which is found in the Scientific Library of thisoifice.

The American Institute 01' Mining and Metallurgical Engineers T. P. 1074found in Mining Technology."

1. A PROCESS FOR BENEFICIATION OF IRON COMPOUND-CONTAINING PHOSPHATEROCK SELECTED FROM THE GROUP CONSISTING OF MONTANA AND TENNESSEEPHOSPHATE ROCK HAVING THE IRON COMPOUNDS UNEVENLY DISPERSED THROUGH THEPHOSPHATE MATERIAL AS A COMPONENT WHICH ECONOMICAL COMMINUTION METHODSFAIL TO LIBERATE, WHICH COMPRISES DESLIMING THE COMMINUTED ORE, ROASTINGTHE COMMINUTED ORE IN A REDUCING ATMOSPHERE AT A TEMPERATURE IN THERANGE OF BETWEEN ABOUT 750* F. AND ABOUT 1350* F., AND SUBJECTING THEROASTED ORE TO MAGNETIC SEPARATION TO PRODUCE AT LEAST A PHOSPHATEFRACTION LOW IN IRON CONTENT.